In a matched-case analysis of data on nearly 30,000 American women with breast cancer, the absolute difference in 5-year survival rate shrank from 12.9 percentage points (95% CI 11.5-14.5) in patients matched by age, year of diagnosis, and clinical site to 4.4 points (95% CI 2.8-5.8) after additional matching for characteristics at presentation, including comorbidities and tumor characteristics, according to Jeffrey Silber, MD, PhD, of Children's Hospital of Philadelphia, and colleagues.

Matching patients for treatments received cut the difference to 3.6 percentage points (95% CI 2.3-4.9), indicating that differences in treatment were responsible for only 0.8 of the 12.9 percentage-point difference between black and white women, the researchers reported in the July 24/31 issue of the Journal of the American Medical Association.

The data also indicated that these patterns held constant from 1991 to 2005, the period of analysis in the study.

"White women who presented like black women (i.e., were matched on demographics and presentation) but who received treatment similar to that received by white women fared almost the same as white women who presented like black women and who were treated in the same way as black women," Silber and colleagues wrote.

In an accompanying editorial, three other researchers indicated that the study's methodology was not entirely free of flaws, but that the overall conclusion was probably correct.

"Ultimately, for any cancer control strategy to succeed, improved care quality appears to be a necessary, but not sufficient condition to eliminate race-based mortality differences in the U.S.," wrote Jeanne Mandelblatt, MD, of Georgetown University in Washington, D.C., and colleagues.

In the context of cancer survival, the possible contributors include differences in the underlying biology, in the time to diagnosis, and in treatment. Teasing these apart and determining whether such differences stem from racial discrimination, socioeconomic status, or other factors has been a continuing challenge.

The current study examined data from the CDC's Surveillance, Epidemiology, and End Results (SEER) database linked with Medicare records. These data covered 7,375 black women diagnosed from 1991 to 2005 at 16 SEER sites who were matched with three sets of 7,375 white women each, all with a mean age of about 76 at diagnosis.

These control sets of white patients were matched to the black patients on the basis of demographics (age, year of diagnosis, and SEER site), characteristics at presentation (comorbidities, tumor size, tumor grade and stage, and estrogen receptor status), and treatment (case characteristics plus details of surgery, radiation treatment, and drug therapy).

In the comparison of black patients with whites matched by demographics only, 5-year survival rates were 55.9% (95% CI 54.8%-57.0%) in the former versus 68.8% (95% CI 67.8%-69.9%) in the latter (P<0.001), Silber and colleagues found.

But 5-year survival in the white set matched by characteristics at presentation was 60.3% (95% CI 59.2%-61.4%), reducing the racial disparity markedly.

Treatments differed significantly between blacks and the presentation-matched white patients. For example, black patients were less likely to receive breast-conserving surgery plus radiation (14.5% versus 16.5%) or chemotherapy with a taxane (3.7% versus 5%), and were more likely to receive no treatment at all (12.6% versus 8.2%) -- all with P-values of less than 0.001.

However, these differences appeared to have less influence on survival rates than differences at presentation.

One factor that may have contributed to that finding was that care received in the 6 to 18 months prior to diagnosis was clearly inferior in the black patients. Rates of specific types of primary and preventive care during this interval were as follows (all P<0.001 for whites versus blacks):

On the other hand, many more of the black patients than the demographic-matched whites had important comorbidities at presentation including diabetes (26% versus 15.3%) and congestive heart failure (9.6% versus 5.9%, P<0.001 for both comparisons).

Black patients also were less likely to have estrogen receptor-positive tumors (53% versus 64.5%, P<0.001).

Another analysis suggested that socioeconomic status was the chief driver of the survival disparity, Silber and colleagues indicated. In a model using data from the black patients and the whites matched by presentation plus treatment characteristics, and then adjusted for dual eligibility status in Medicaid and Medicare, the hazard ratio for death was a nonsignificant 1.02 (95% CI 0.97-1.09).

A similar analysis adjusting the mortality data for poverty rates and educational attainment in patients' census tracts also found similar survival rates in black and white patients after matching for presentation and treatment.

Overall, Silber and colleagues wrote, "Most of the [survival] difference is explained by poorer health of black patients at diagnosis, with more advanced disease, worse biological features of the disease, and more comorbid conditions."

'Synergy Between Presentation and Treatment'

In the accompanying editorial, Mandelblatt and colleagues cautioned against reading too much into the study findings. They noted that the data lacked detail on chemotherapy doses and total drug exposure and were entirely absent with respect to hormone therapy. Also, Silber and colleagues did not account for the variable benefit from chemotherapy with age and disease stage.

The editorialists also argued that the study's sequential matching strategy might have affected the findings, noting that "because there is a synergy between presentation and treatment, it is difficult to disentangle their separate effects from this type of analysis."

The study was funded by the Agency for Healthcare Quality and Research, the Department of Health and Human Services, and the National Science Foundation.

Study authors and the editorialists declared they had no relevant financial interests.

John Gever, Managing Editor, has covered biomedicine and medical technology for more than 30 years. He holds a B.S. from the University of Michigan and an M.S. from Boston University. He is now based in Pittsburgh. In addition to his administrative duties, he covers neurology and psychiatry for MedPage Today.

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